The present invention relates to a tubular element and a method for manufacturing thereof. The tubular element has an inner space forming a passage for conducting milk, wherein the tubular element constitutes a first material portion which contains the main part of the tubular element and an additional material portion which includes a vent passage adapted to supply air to the inner space of the tubular element and wherein the first material portion and the additional material portion are arranged in contact with each other in a contact area.
A cluster for milking of animals comprises several teat cups and a corresponding number of short milk tubes each connected to a teat cup. Each teat cup includes a liner and a rigid shell forming a pulsation chamber. The liner and the short milk tube define a milk passage for conducting milk from a teat to a claw of the cluster. During a milking process, a substantially constant vacuum is applied to the milk passage at the same time as a pulsating vacuum is transferred to the pulsation chamber. During periods when vacuum is transferred to the pulsation chamber, the liner expands and causes a pressure drop in the upper part of the milk passage. If at the same time an abundant flow of milk is present in the milk passage, there is risk that milk will be sucked backwards in the milk passage to the teat. Such a backflow of milk is undesired by several reasons.
U.S. Pat. No. 6,055,931 shows an air vent plug adapted to be inserted through a hole in a wall of a milk tube. The air vent plug has an outer flange engaging an outer surface of the milk tube, a barrel extending through the wall of the milk tube, a tip portion engaging an inner surface of the milk tube and a vent passage extending through the vent plug. The vent passage is dimensioned to allow supply of air into the milk passage of the milk tube. The existence of the vent plug eliminates the risk of back flow of milk in the milk passage. However, the outer flange of the vent plug projects out from the outer surface of the milk tube and the tip portion projects into the milk passage. This parts of the vent plug provides spaces and corners in the vicinity of the vent passage in which dirt and milk residues can be caught. It is a risk that colonies of bacteria can be grown in such spaces and corners.